1. Field
This disclosure relates to waveguide devices that support two orthogonal modes. Specifically, this disclosure relates to ortho-mode transducers.
2. Description of the Related Art
An ortho-mode transducer (OMT) is a three-port waveguide device having a common waveguide coupled to two branching waveguides. Within this description, the term “port” refers generally to an interface between devices or between a device and free space. A port may include an interfacial surface, an aperture in the interfacial surface to allow microwave radiation to enter or exit a device, and provisions to mount or attach an adjacent device.
The common waveguide of an OMT typically supports two orthogonal linearly polarized modes. Within this document, the terms “support” and “supporting” mean that a waveguide will allow propagation of a mode with little or no loss. The common waveguide terminates at a common port aperture. The common port aperture is defined by the intersection of the common waveguide and an exterior surface of the OMT.
Each of the two branching waveguides of an OMT typically support only a single linearly polarized mode. The mode supported by the first branching waveguides is orthogonal to the mode supported by the second branching waveguide. In a typical OMT, a first branching waveguide is axially aligned with the common waveguide. A second branching waveguide is typically normal to the common waveguide. Within this document, the term “orthogonal” will be reserved to describe the polarization direction of modes, and “normal” will be used to describe geometrically perpendicular structures.
The branching waveguide that is axially aligned with the common waveguide terminates at what is commonly called the vertical port. The linearly polarized mode supported by the vertical port is commonly called the vertical mode. The branching waveguide which is normal to the common waveguide is terminated at what is commonly called the horizontal port. The branching waveguide that terminates at the horizontal port also supports only a single polarized mode commonly called the horizontal mode.
The terms “horizontal” and “vertical” will be used in this document to denote the two orthogonal modes and the waveguides and ports supporting those modes. Note, however, that these terms do not connote any particular orientation of the modes or waveguides with respect to the physical horizontal and vertical directions.
An example prior art OMT is shown in FIG. 1A and FIG. 1B. FIG. 1A is a perspective view of the prior art OMT showing the common port, labeled PORT 1. The common port includes a common port aperture defined by the intersection of the common waveguide and the surface, or face, of the common port. The common port aperture may have a square, as shown, or circular cross section, or other shape that supports two orthogonal modes. In FIG. 1A, the common port aperture is centered in a circular flange with six holes for attaching the adjacent waveguide structure (not shown). The flange may be circular, square, rectangular or other shape. The flange may have more, fewer, or no attachment holes.
FIG. 1B is a different perspective view of the same prior art OMT device. PORT 2 is the vertical port that terminates the branching waveguide that is axially aligned with the common waveguide. PORT 2 includes a vertical port aperture at or near the center of a generally square mounting flange. PORT 3 is the horizontal port that terminates the branching waveguide that is normal to the common waveguide. PORT 3 includes a horizontal port aperture at or near the center of a generally square mounting flange. The horizontal port aperture and the vertical port aperture may be rectangular in cross-section, as shown, or may be elliptical or other shape that supports a single polarization mode. The cross-sectional shape of the horizontal port aperture and the vertical port aperture may be different. The mounting flanges of PORT 2 and PORT 3 may be square, round, or other shape. The mounting flanges may have more, fewer, or no attachment holes. The mounting flanges for PORT 2 and PORT 3 may be different.
An OMT is a versatile device that may be used in a variety of applications where two orthogonally polarized signals are simultaneously guided through the OMT. The OMT can be designed to support one frequency band, two distinctly different bands, or overlapping frequency bands by the appropriate design of the orthogonal branching waveguides. For example, a common application of the OMT is in X-band or Ku-band satellite communication systems where an OMT may be positioned behind a satellite reflector antenna. The OMT may simultaneously guide a vertically polarized transmitted signal from the vertical port to the antenna and guide a horizontally polarized received signal from the antenna to a receiver via the horizontal port.